High melting ptfe polymers for melt-processing

ABSTRACT

Provided are a tetrafluoroethylene copolymers having a melting point of at least 317° C., a melt flow index (MFI) at 372° C. and a 5 kg load (MFI 372/5) of from about 0.60 g/10 min up to about 15 g/10 min. Also provided are methods of forming a shaped article using the copolymers described above, shaped articles made with those copolymers and compositions containing such copolymers.

FIELD

The present disclosure relates to tetrafluoroethylene copolymers, inparticular melt processable tetrafluoroethylene copolymers withsufficient mechanical properties to make shaped articles, methods ofmaking shaped articles and methods of melt-processingtetrafluoroethylene copolymers.

BACKGROUND

Polytetrafluoroethylenes (PTFE's, also often referred to aspolytetrafluoroethylenes) have found wide application due to their highchemical inertness, low friction properties, non-stick properties, highmelting points and thus high service temperatures and thermal stability.These properties have made PTFE's a well known material and the materialof choice for making protective coatings, sealing materials like valves,washers and O-rings, implants, insulators, membranes, films, gaskets foruse in household applications, architecture, and medical, chemical,aircraft and automotive industry.

According to international industry standards tetrafluoroethylene (TFE)homopolymers and copolymers with up to 1% by weight of otherperfluorinated monomers can be called PTFE (see, for example, DIN EN ISO12086-1). Furthermore, the polymers must have melting point within therange of 327+/−10° C. to qualify as PTFE.

To make shaped articles from PTFE, the polymers need to have sufficientmechanical properties, such as a tensile strength of at least 10 MPa andan elongation at break of at least 20%. Otherwise, the materials are toobrittle to be shaped into articles. To have such mechanical propertiesthe PTFE polymers must have a sufficiently high molecular weight,typically about 10⁶ g/mole or greater. However, PTFE polymers at suchhigh molecular weight also have a very high melt viscosity (about10¹⁰-10¹³ Pa·s at 380° C.). This results in PTFE having a melt flowindex (MFI) of less than 0.1 g/10 min at 372° C. using a 5 kg load (MFI372/5 of 0 g/10 min).

The MFI measures the amount of polymer that can be pushed through a dieat a specified temperature (here 372° C.) using a specified weight (here5 kg). Thus, the MFI is a measure for the suitability formelt-processing of a polymer. Fluoropolymers with an MFI (372/5) of lessthan 0.1 g/10 min are considered not melt-processable. They cannot beprocessed from the melt by ordinary melt-processing techniques like, forexample, melt extrusion or injection molding to make shaped articles.

Therefore, to make shaped articles from PTFE special processingtechniques have to be used, like ram extrusion or cold compressionmolding and sintering. Typically, PTFE's are processed by preparingblocks, which are then sintered to fuse the polymer particles. Thesintered billets are then skived or machined into shaped articles. Thesetechniques may lead to inhomogeneous products containing cavities as aresult of imperfect fusion of the PTFE particles during sintering.Furthermore, machining and skiving methods are economically inefficientbecause they produce considerable amounts PTFE waste.

Therefore, attempts have been made to prepare fluoropolymers that aremelt processable.

One attempt is the production of low molecular weightpolytetrafluoroethylene, so-called “PTFE micropowders”. PTFEmicropowders have a high melting point like high molecular PTFEs buthave a much lower melt viscosity (typically far below 10⁵ Pa·s. at 382°C.). They have an MFI (372/5) of greater 0.1 g/10 mins and theoreticallycould be processed from the melt. However, PTFE micropowders are brittleand do not have mechanical properties suitable for making shapedarticles. Micropowder material formed by melt processing breaks uponcooling or cannot be released from the mold without breaking PTFEmicropowders thus do not have any mechanical properties suitable formaking shaped PTFE articles. Therefore, PTFE micropowders are used assolid lubricants or as additives to impart low friction or low energysurface properties to other polymers. PTFE micropwoders are commerciallyavailable under the trade designation “Dyneon TF 9201” or “Dyneon TF9207” from Dyneon LLC, Oakdale, Minn., USA or under the tradedesignation Zonyl (e.g. Zonyl 1000, Zonyl 1100, Zonyl 1200, Zonyl 1400,and Zonyl 1500) from DuPont de Nemours, Wilmington, Del., US.

Another attempt of providing melt-processable fluoropolymers involvescopolymerising comparatively high amounts of perfluoro alkyl vinylethers (PAVE's) with TFE. Typical amounts of copolymers range from 1 to5 mol % (which corresponds to 1.7% to 8.4% wt % in case of perfluoromethyl vinyl ether (PMVE)—the smallest of the perfluoro alkyl vinylethers). These types of fluoropolymers are referred to in the art as“PFA's”. PFA's have a molecular weight of 1 to 5×10⁵ g/mol and a meltingpoint between 300 and 315° C. (compare Modern Fluoropolymers, JohnSchiers, Wiley& Sons New York, 1998, pp 223 to 232). PFA's aremelt-processable with sufficient mechanical properties to make shapedarticles. However, due to their lower melting point they have a lowerservice temperature and thermal stability than PTFE's.

In U.S. Pat. No. 6,531,559 and U.S. Pat. No. 7,160,623 to Smith et al.another attempt to provide melt-processable PTFE's which melting pointsgreater than 320° C. has been described. According to these documentssuch polymers may be prepared by blending various PTFE grades ofdifferent molecular weight and MFI's. While some of those blends arereported to be melt-proccessable and are reported to be releasable frommolds without breaking these materials tend to be inhomogeneous and maythus be disadvantageous. U.S. Pat. Nos. 6,531,559 and 7,160,623 alsoappear to suggest making a TFE-comonomer with hexafluoropropene (HFP) ora perfluoro alkyl vinyl ether (PAVE) in amounts of less than 3 or lessthan 0.5 mole % for producing a melt-processable PTFE. However, whilethese documents provide examples for PTFE blends they do not provide anydescription of how such melt-processable copolymers can be prepared nordo they provide any examples of such copolymers. Indeed, when using HFPor a PAVE as comonomers with TFE in amounts as low as 1.0% wt. theresulting polymers with melting points greater than 315° C. were foundto be so brittle that mechanical properties like tensile strength orelongation at break could not even be measured (see comparative examplesherein below). Therefore, such copolymers could not be used to makeshaped articles

SUMMARY

There is a need to provide tetrafluoroethylene polymers that have amelting point of at least 317° C., preferably at least 319° C. and morepreferably at least 321° C. but that are melt-processable, i.e. thathave a melt flow index at 372° C. and a 5 kg load (MFI (372/5)) ofgreater than 0.1 g/10 min. Desirably, such polymers are suitable formelt-processing such as melt extrusion and thus have an MFI(372/5) of atleast 0.60 g/10 min. Such polymers are required to have sufficientmechanical properties for making shaped articles, such as an elongationat break of at least 20% and a tensile strength of at least 10 MPa. Ithas now been found that such polymers can be prepared when specificalkoxy or polyoxyalkyl substituted perfluorinated vinyl or allyl etherare used as comonomers in specific amounts to give tetrafluoroethylenecopolymers of a specific MFI (372/5) range. Therefore, in the followingthere are provided tetrafluoroethylene copolymers comprising repeatingunits derived from tetrafluoroethylene (TFE) and having a melting pointof at least 317° C., a melt flow index (MFI) at 372° C. and a 5 kg load(MFI 372/5) of from about 0.60 g/10 min up to about 15 g/10 min, andcomprising from 0.12 to 1.40% by weight based on the weight of thecopolymer of units derived from one or more perfluorinated comonomersand wherein the perfluorinated comonomers comprise one or moreperfluorinated alkyl vinyl or alkyl allyl ether wherein the alkyl groupof vinyl or allyl ether is interrupted by at least one oxygen atom.

In another aspect there is provided a method of making a shaped articlecomprising:

providing a composition comprising a copolymer as described above andsubjecting the composition to melt-processing selected from meltextrusion, melt spinning, injection molding and melt blowing.

In a further aspect there is provided a shaped article comprising thepolymer as described above.

In yet another aspect there is provided a composition comprising apolymer as described above wherein the composition is an aqueousdispersion.

In a further aspect there is provided a method of makingtetrafluoroethylene copolymers that are melt-processable and have anelongation at break of at least 20% and a tensile strength at break ofat least 10 MPa and a melting point of at least 317° C., or at least319° C., or at least 321° C., and an MFI (375/5) of from about 1 toabout 15 g/10 min comprising: polymerising TFE in an aqueous medium inthe presence of an effective amount of a perfluorinated comonomer asdescribed herein.

Advantageously, the copolymers provided herein may contain asufficiently amount of comonomers to qualify as PTFE.

DETAILED DESCRIPTION

Before any embodiments of this disclosure are explained in detail, it isto be understood that the disclosure is not limited in its applicationto the details of construction and the arrangement of components setforth in the following description. The invention is capable of otherembodiments and of being practiced or of being carried out in variousways. Also, it is to be understood that the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. Contrary to the use of “consisting”, which is meant to belimiting, the use of “including,” “containing”, “comprising,” or“having” and variations thereof is meant to be not limiting and toencompass the items listed thereafter as well as additional items. Forexample, a composition containing an ingredient A is meant to contain Aor A and other ingredient. A composition consisting of A is meant tohave ingredient A but no other ingredient. In both cases (limiting ornon limiting meaning) equivalents are meant to be included.

The use of “a” or “an” is meant to encompass “one or more”.

Any numerical range recited herein is intended to include all valuesfrom the lower value to the upper value of that range. For example, aconcentration range of from 1% to 50% is intended to be an abbreviationand to expressly disclose the values between the 1% and 50%, such as,for example, 2%, 40%, 10%, 30%, 1.5%, 3.9% and so forth.

The term “perfluorinated” as used herein refers to a compound whosehydrocarbons have been completely replaced by F atoms. For example, a—CF₃ residue is a perfluorinated methyl residue. A —CHF₂ residue forexample would be a “partially fluorinated” compound, or morespecifically a partially fluorinated methyl group. A perfluorinatedcompound may, however, in addition to C and F atoms also contain Oatoms. Those O atoms are ether functionalities and are also referred toas “catenary oxygen atoms” as they are part of an alkyl chain and, morespecifically, interrupting it. With respect to polymers the term“perfluorinated” is used to indicate that the polymers is made up byunits derived from perfluorinated momomers. It is to be understood thatperfluorinated polymers may still contain small amounts of hydrogens,typically in end groups which may be generated for example by chaininterruptions or by degradation reactions of unstable endgroupsgenerated in the polymerisation.

The present disclosure provides melt-processable tetrafluoroethylenepolymers that have sufficient mechanical strength to be formed intoshaped articles from the melt and that mechanical properties, such aselongation at break and/or tensile strength of samples generated fromthe melt can be determined.

The polytetrafluoroethylenes of the present disclosure are copolymers ofTFE (i.e., comprising interpolymerized units of TFE and at least oneadditional perfluorinated monomer which is a perfluorinated vinyl orally ether containing an alkyl group that is interrupted by at least oneoxygen atom, as will be described in greater detail below and which willbe referred to in the following as “the perfluorinated comonomer”. Theamount of perfluorinated comonomers used to prepare the polymersdescribed herein should not exceed amounts of more than 1.4% wt,preferably less than 1.0% by weight, more preferably less than 0.9% byweight based on the weight of the copolymer. Accordingly, the totalamount of the perfluorinated comonomer(s) may not exceed 0.95% or 0.75%by weight based on the total weight of the copolymer. The remainder ofthe copolymer are preferably units derived from TFE. In this case thepolymers may qualify as PTFE's according to industry standards. However,it is also contemplated that in addition to TFE and the perfluorinatedcomonomers other comonomers may be used. For example, but not limitedthereto, in some embodiments up to 30% of the units derived from TFE maybe replaced by chlorotrifluoroethylene.

It is understood that more than one of the perfluorinated comonomers maybe used, for example combinations thereof may be used. In such cases,the total amounts of the perfluorinated comonomers should not exceedthose described above. However, the additional perfluorinated comonomersshould not be present in amounts of less than 0.10 or less than 0.12 orless than 0.14% by weight or less than 0.20% by weight. If used in loweramounts polymers having mechanical properties described herein and alsohaving a melting point of greater than 317° C., or greater than 319° C.,or greater than 321° C. and that are also melt processable may not beobtained.

Suitable perfluorinated comonomers are perfluorinated compounds havingone or at least one vinyl and/or allyl ether groups and a perfluorinatedalkyl residue linked to the ether oxygen that is interrupted by at leastone oxygen atom.

Examples of suitable comonomers include those corresponding to thegeneral formulae

CF₂═CF—(CF₂)_(n)—O—Rf  (I),

or

CF₂═CF—(CF₂)_(n)—O—Rf′—O—(CF₂)_(m)—CF═CF₂  (II).

In formula (I) n represents either 0 or 1. Rf represents a linear orbranched, cyclic or acyclic perfluorinated alkyl residue containing atleast one catenary oxygen atom. Rf may contain up to 8, preferably, orup to 6 carbon atoms, such as 1, 2, 3, 4, 5 and 6 carbon atoms. Typicalexamples of Rf include linear, branched alkyl residues interrupted byone oxygen atom, and linear or branched alkyl residues containing 2, 3,4 or 5 ether oxygen atoms. Further examples of Rf include residuescontaining one or more of the following units and combinations thereof:

—(CF₂O)—, —(CF₂CF₂—O)—, (—O—CF₂)—, —(O—CF₂CF₂)—, —CF(CF₃)—,—CF(CF₂CF₃)—, —O—CF(CF₃)—, —O—CF(CF₂CF₃)—, —CF(CF₃)—O—, —CF(CF₂CF₃)—O—.Further examples of Rf include but are not limited to:

-   —(CF₂)_(r1)—O—C₃F₇,-   —(CF₂)_(r2)—O—C₂F₅,-   —(CF₂)_(r3)—O—CF₃,-   —(CF₂—O)_(s1)—C₃F₇,-   —(CF₂—O)_(s2)—C₂F₅,-   —(CF₂—O)_(s3)—CF₃,-   —(CF₂CF₂—O)_(t1)—C₃F₇,-   —(CF₂CF₂—O)_(t2)—C₂F₅,-   —(CF₂CF₂—O)_(t3)—CF₃,    wherein r1 and s1 represent 1, 2, 3, 4, or 5, r2 and s2 represent 1,    2, 3, 4, 5 or 6, r3 and s3 represent 1, 2, 3, 4, 5, 6 or 7; t1    represents 1 or 2; t2 and t3 represent 1, 2 or 3.

Specific examples of suitable perfluorinated comonomers include

-   F₂C═CF—O—CF₂—O—(CF₂)—F,-   F₂C═CF—O—CF₂—O—(CF₂)₂—F,-   F₂C═CF—O—CF₂—O—(CF₂)₃—F,-   F₂C═CF—O—CF₂—O—(CF₂)₄—F,-   F₂C═CF—O—(CF₂)₂—OCF₃,-   F₂C═CF—O—(CF₂)₃—OCF₃,-   F₂C═CF—O—(CF₂)₄—OCF₃,-   F₂C—CF—CF₂—O—(CF₂)₃—(OCF₂)₂—F,-   F₂C═CF—CF₂—O—CF₂—(OCF₂)₃—CF₃,-   F₂C═CF—CF₂—O—CF₂—(OCF₂)₄—CF₃,-   F₂C═CF—CF₂—O—(CF₂O)₂—OCF₃,-   F₂C═CF—CF₂—O—(CF₂O)₃—OCF₃,-   F₂C═CF—CF₂—O—(CF₂O)₄—OCF₃.

In formula (II) n and m represent, independently from each other, either1 or 0. Rf′ represents a linear, branched, cyclic or acyclicperfluorinated alkylene unit that may or may not contain one or morecatenary oxygen atoms. Rf′ may have up to 8, preferably up to 6 carbonatoms. Typical examples of Rf′ include linear or branched alkylenescontaining one or more —(CF₂O)— or —(CF₂CF₂—O)— units. Further examplesfor Rf′ include but are not limited to

-   —(CF₂)_(u)-   —(CF₂)_(o)—CF(CF₃)—(CF₂)_(q)—-   —(CF₂)_(o)—CF(C₂F₅)—(CF₂)_(q)—    wherein u represents 1, 2, 3, 4, 5, 6, 7 or 8; o represents 0, 1, 2,    3, 4, 5, 6, q represents 0, 1, 2, 3, 4, 5, 6 with the proviso that    o+q is 6 or less.

Specific examples of suitable perfluorinated comonomers further include

-   F₂C═CF—O—X—O—CF═CF₂,-   F₂C═CF—O—X—O—CF₂—CF═CF₂,-   F₂C═CF—CF₂—O—X—O—CF₂—CF═CF₂, wherein X is (CF₂)n and n is 1, 2, 3,    4, 5, 6, 7 or 8.

Perfluorinated comonomers as described above are either commerciallyavailable, for example from Anles Ltd. St. Peterburg, Russia or can beprepared according to methods described in EP 1 240 125 to Worm et al.,or EP 0 130 052 to Uschold et al. or in Modern Fluoropolymers, J.Scheirs, Wiley 1997, p 376-378.

Copolymers, especially those with a vinyl functionality, having aresidue Rf with only one catenary oxygen atom preferably have acomonomer content of at least 0.20% by weight based on the weight of thecopolymer.

The tetrafluoroethylene copolymers provided herein have a melting pointof at least 317° C. or at least 319° C. or at least 321° C. Typically,the polymers have a melting point between 321° C. and 329° C. Whenreferred herein to a melting point the melting point of the once moltenmaterial is meant unless stated otherwise. Polymers with a very highcontent of TFE-units tend to have different melting points when beingmolten for the first time and after being molten for the first time, inwhich case the melting point tends to be somewhat lower. However, oncethe material has been molten the melting point remains constant. Thedetermination of the melting point by DSC has been described, forexample, in ASTM D 4591.

The tetrafluoroethylene copolymers provided herein have an MFI (372/5)of from about 0.6 g/10 min. up to about 15 g/10 min. Outside this rangethe polymers may be too brittle to have a measurable tensile strengthand/or elongation. The determination of the MFI has been described, forexample, in DIN EN ISO 1133.

In one embodiment of this disclosure the perfluorinated comonomer is acompound according to formula (I) wherein Rf has only one oxygen atomand n is 1 or 0. In this embodiment the copolymers have a content ofperfluorinated comonomer of from about 0.20% by weight up to about 1.4%by weight or up to about 1.0% by weight or up to about 0.95% by weight.The copolymers of this embodiment may further have an MFI (372/5) offrom about 0.60 to about 15 g/10 min, preferably from about 0.7 to about6 g/10 min or from about 0.8 to 5 g/10 min and have a melting point ofat least 319° C. or preferably at least 321° C.

In yet another embodiment the perfluorinated comonomer is a compoundaccording to formula (I) wherein Rf has at least two catenary oxygenatoms, wherein n is 1 or 0 and is preferably 1. In this embodiment thecopolymers have a content of perfluorinated comonomer of from about0.10% by weight up to about 1.4% by weight or from about 0.14% by weightup to about 1.0% by weight or up to about 0.95% by weight. Thetetrafluoroethylene copolymers of this embodiment further have an MFI(372/5) of from about 0.60 to about 15, preferably from about 1 to about14 or to about 12 and have a melting point of at least 319° C. orpreferably at least 321° C.

The tetrafluoroethylene copolymers described herein have mechanicalproperties sufficient to prepare shaped articles by melt processing.This means the copolymers have a tensile strength of at least 10 MPa orat least 20 MPa. The copolymers provided herein have an elongation atbreak of at least 20% or at least 100% or even at least 200%. Thedetermination of elongation at break and tensile strength has beendescribed, for example, in DIN EN ISO 527-1.

The tetrafluoroethylene copolymers described herein may be prepared byemulsion or suspension polymerisation. TFE is copolymerized in thepresence of initiators and perfluorinated comonomers described above.Other ingredients may be added.

The perfluorinated comonomers are used in effective amounts to makepolymer with the properties described herein. Effective amounts are atleast those amounts of perfluorinated comonomers as described andexemplified above.

In a suspension polymerisation the reaction mixture coagulates andsettles as soon as stirring of the reaction mixture is discontinued.Suspension polymerisations are carried out in the absence ofemulsifiers. Usually vigorously stirring is required.

In aqueous emulsion polymerisations the polymerisation is carried out ina way that stable dispersions are obtained. The dispersions remainstable after stirring of the reaction mixture has stopped for at least 2hours, or at least 12 hours or at least 24 hours. Typically, fluorinatedemulsifiers are employed in the aqueous emulsion polymerisation. Whenused, a fluorinated emulsifier is typically used in an amount of 0.01%by weight to 1% by weight based on solids (polymer content) to beachieved. Gently stirring is required if the emulsion polymerisation isto be carried out with out emulsifiers.

Suitable emulsifiers include any fluorinated emulsifier commonlyemployed in aqueous emulsion polymerization. Particularly preferredemulsifiers are those that correspond to the general formula:

Y—R_(f)—Z-M  (III)

wherein Y represents hydrogen, Cl or F; R_(f) represents a linear orbranched perfluorinated alkylene having 4 to 10 carbon atoms; Zrepresents COO⁻ or SO₃ ⁻ and M represents a cation like an alkali metalion, an ammonium ion or H. Exemplary emulsifiers include: ammonium saltsof perfluorinated alkanoic acids, such as perfluorooctanoic acid andperfluorooctane sulphonic acid.

More preferable for use in the preparation of the polymers describedherein are emulsifiers of the general formula:

[R_(f)—O-L-COO⁻]_(i)X_(i) ⁺  (IV)

wherein L represents a linear or branched partially or fully fluorinatedalkylene group or an aliphatic hydrocarbon group, R_(f) represents alinear or branched, partially or fully fluorinated aliphatic group or alinear or branched partially or fully fluorinated group interrupted withone or more oxygen atoms, X_(i) ⁺ represents a cation having the valencei and i is 1, 2 and 3. In case the emulsifier contains partiallyfluorinated aliphatic group it is referred to as a partially fluorinatedemulsifier. Preferably, the molecular weight of the emulsifier is lessthan 1,000 g/mole.

Specific examples are described in, for example, US Pat. Publ.2007/0015937 (Hintzer et al.). Exemplary emulsifiers include:CF₃CF₂OCF₂CF₂OCF₂COOH, CHF₂(CF₂)₅COOH, CF₃(CF₂)₆COOH,CF₃O(CF₂)₃OCF(CF₃)COOH, CF₃CF₂CH₂OCF₂CH₂OCF₂COOH, CF₃O(CF₂)₃OCHFCF₂COOH,CF₃O(CF₂)₃OCF₂COOH, CF₃(CF₂)₃(CH₂CF₂)₂CF₂CF₂CF₂COOH,CF₃(CF₂)₂CH₂(CF₂)₂COOH, CF₃(CF₂)₂COOH,CF₃(CF₂)₂(OCF(CF₃)CF₂)OCF(CF₃)COOH, CF₃(CF₂)₂(OCF₂CF₂)₄OCF(CF₃)COOH,CF₃CF₂O(CF₂CF₂O)₃CF₂COOH, and their salts.

Other emulsifiers include fluorosurfactants that are not carboxylicacids, such as for example, sulfinates or perfluoroaliphatic sulfinatesor sulfonates. The sulfinate may have a formula Rf—SO₂M, where Rf is aperfluoroalkyl group or a perfluoroalkoxy group. The sulfinate may alsohave the formula Rf′—(SO₂M)_(n) where Rf′ is a polyvalent, preferablydivalent, perfluoro radical and n is an integer from 2-4, preferably 2.Preferably the perfluoro radical is a perfluoroalkylene radical.Generally Rf and Rf′ have 1 to 20 carbon atoms, preferably 4 to 10carbon atoms. M is a cation having a valence of 1 (e.g. H+, Na+, K+,NH₄+, etc.). Specific examples of such fluorosurfactants include, butare not limited to C₄F₉—SO₂Na; C₆F₁₃—SO₂Na; C₈F₁₇—SO₂Na; C₆F₁₂—(SO₂Na)₂;and C₃F₇—O—CF₂CF₂—SO₂Na.

In one embodiment, the molecular weight of the emulsifier, preferably apartially fluorinated emulsifier, more preferably a partiallyfluorinated emulsifier having at least one carboxylic acidfunctionality, is less than 1500, 1000, or even 500 grams/mole.

These emulsifiers may be used alone or in combination as a mixture oftwo or more of them. The amount of the emulsifier is well below thecritical micelle concentration, generally within a range of from 250 to5,000 ppm (parts per million), preferably 250 to 2000 ppm, morepreferably 300 to 1000 ppm, based on the mass of water to be used.Within this range, the stability of the aqueous emulsion should besufficient. In order to further improve the stability of the aqueousemulsion, it may be preferred to add one or more emulsifiers during orafter the polymerization. The amount of emulsifier used my influence theshape of the polymer particles formed. Higher amounts of emulsifiers, inparticular amounts above the cmc may lead to the generation of elongatedparticles like rod-shaped or ribbon-shaped particles. Lower amounts ofemulsifiers may lead to spheroidal or spherical particles.

In one embodiment, the emulsifier is not added simultaneously (i.e., isadded separately) with the fluorinated polyether to the reaction vessel.

In one embodiment, the emulsifier is added as a microemulsion with afluorinated liquid, such as described in U.S. Publ. No. 2008/0015304(Hintzer et al.), WO Publ. No. 2008/073251 (Hintzer et al.), and EP Pat.No. 1245596 (Kaulbach et al.). Microemulsions are transparent emulsionsthat are thermodynamically stable (stable for longer than 24 hours) andhave droplet sizes from 10 nm to a maximum of 100 nm. Large quantitiesof fluorinated emulsifiers are used to prepare these microemulsions. Inthe cases where a mixture is used that is not a microemulsion, theparticle sizes and amounts of the ingredients are such that the emulsionor mixture formed is not transparent, but is milky or opaque to thevisible eye.

In one embodiment, the emulsifier is not added as a microemulsion with afluorinated liquid. Typical fluorinated liquids include fluorinated orperfluorinated hydrocarbons or fluorinated or perfluorinated ether orpolyether. The fluorinated polyether may be added in excess of theemulsifier. In one embodiment, the weight ratio of the fluorinatedpolyether to emulsifier is greater than 1:1, 1.5:1, 2:1, 2.5:1, 3:1,5:1, or even 10:1.

Therefore, in one embodiment there is provided a tetrafluoroethylenecopolymer as described herein in an aqueous dispersion, typically in anamount of 10 to 70% b weight (solid content) and in the presence of atleast one emulsifier, preferably of the type as described in formula(IV).

The aqueous emulsion polymerization may be initiated with a free radicalinitiator or a redox-type initiator. Any of the known or suitableinitiators for initiating an aqueous emulsion polymerization of TFE canbe used. Suitable initiators include organic as well as inorganicinitiators, although the latter are generally preferred. Exemplaryorganic initiators include: organic peroxide such as bissuccinic acidperoxide, bisglutaric acid peroxide, or tert-butyl hydroperoxide.Exemplary inorganic initiators include: ammonium-alkali- or earth alkalisalts of persulfates, permanganic or manganic acids, with potassiumpermanganate preferred. A persulfate initiator, e.g. ammonium persulfate(APS), may be used on its own or may be used in combination with areducing agent. Suitable reducing agents include bisulfites such as forexample ammonium bisulfite or sodium metabisulfite, thiosulfates such asfor example ammonium, potassium or sodium thiosulfate, hydrazines,azodicarboxylates and azodicarboxyldiamide (ADA). Further reducingagents that may be used include sodium formaldehyde sulfoxylate orfluoroalkyl sulfinates. The reducing agent typically reduces thehalf-life time of the persulfate initiator. Additionally, a metal saltcatalyst such as for example copper, iron, or silver salts may be added.

The amount of the polymerization initiator may suitably be selected, butit is usually preferably from 2 to 600 ppm, based on the mass of waterused in the polymerisation. The amount of the polymerization initiatorcan be used to adjust the MFI of the tetrafluoroethylene copolymers. Ifsmall amounts of initiator are used a low MFI will be obtained. The MFIcan also, or additionally, be adjusted by using a chain transfer agent.Typical chain transfer agents include ethane, propane, butane, alcoholssuch as ethanol or methanol or ethers like but not limited to dimethylether, tert butyl ether, methyl tert butyl ether. The amount and thetype of perfluorinated comomonomer influences the melting point of theresulting polymer.

The aqueous emulsion polymerization system may further compriseauxiliaries, such as buffers, and complex-formers. It is preferred tokeep the amount of auxiliaries as low as possible to ensure a highercolloidal stability of the polymer latex. The aqueous emulsionpolymerization may further comprise additional comonomers if desired. Inone embodiment, the polymerization is initiated with TFE monomers andcomonomers to form the tetrafluoroethylene compolymers.

In another embodiment, a seeded polymerization is used to produce thetetrafluoroethylene copolymers. If the composition of the seed particlesis different from the polymers that are formed on the seed particles acore-shell polymer is formed. That is, the polymerization is initiatedin the presence of small particles of fluoropolymer, typically smallPTFE particles that have been homopolymerized with TFE or produced bycopolymerizing TFE with one or more perfluorinated comonomers asdescribed above. These seed particles typically have a Z-averagediameter of between 50 and 100 nm or 50 and 150 nm (nanometers). Suchseed particles may be produced, for example, in a separate aqueousemulsion polymerization. They may be used in an amount of 20 to 50% byweight based on the weight of water in the aqueous emulsionpolymerization. Accordingly, the thus produced particles will comprise acore of a homopolymer of TFE or a copolymer of TFE and an outer shellcomprising either a homopolymer of TFE, or a copolymer of TFE. Thepolymer may also have one or more intermediate shells if the polymercompositions are varied accordingly. The use of seed particles allowsbetter control over the resulting particle size and the ability to varythe amount of TFE in the core or shell. Such polymerization of TFE usingseed particles is described, for example, in U.S. Pat. No. 4,391,940(Kuhls et al.) or WO03/059992 A1. In another embodiment, core shellparticles may be used which comprise a core of a homopolymer of TFE or acopolymer of TFE, and at least one shell comprising either a homopolymerof TFE, or a copolymer of TFE, wherein the at least one outer shell hasa molecular weight that is lower than that of the core. The core shellstructure described above may further increase the resistance of thepolymer to coagulation.

Again the polymer has the final composition regarding the nature andamounts of comonomers as described herein above.

The aqueous emulsion polymerization, whether done with or without seedparticles, will preferably be conducted at a temperature of at least 10°C., 25° C., 50° C., 75° C., or even 100° C.; at most 70° C., 80° C., 90°C., 100° C., 110° C., 120° C., or even 150° C. The polymerization willpreferably be conducted at a pressure of at least 0.5, 1.0, 1.5, 1.75,2.0, or even 2.5 MPa (megaPascals); at most 2.25, 2.5, 3.0, 3.5, 3.75,4.0, or even 4.5 MPa.

Usually the aqueous emulsion polymerization is carried out by mildlystirring the aqueous polymerization mixture. The stirring conditions arecontrolled so that the polymer particles formed in the aqueousdispersion will not coagulate. The aqueous emulsion of the presentdisclosure may be carried out in a vertical kettle (or autoclave) or ina horizontal kettle. Paddle or impeller agitators may be used.

The aqueous emulsion polymerization usually is carried out until theconcentration of the polymer particles in the aqueous emulsion is atleast 15, 20, 25, or even 30% by weight; at most 20, 30, 35, 40, or even50% by weight (also referred to a solid content).

In the resulting dispersion, the average particle size of the polymerparticles (i.e., primary particles) is at least 150, 200, or even 250nm; at most 250, 275, 300, or even 350 nm (Z-average). The particlesizes of dispersions can be determined by inelastic light scattering.

The polymer dispersion can also be used to prepare dispersions withbimodal, and multimodal particle size distributions for example bymixing different dispersions. These distributions may have a widedistribution, such as, for example, particle sizes ranging from 20 nm to1000 nm as disclosed in e.g. U.S. Pat. No. 5,576,381, EP 0 990 009 B1and EP 969 055 A1. Multi-modal fluoropolymer particle dispersions maypresent advantageous properties in coatings, such as better adhesion tothe substrate and denser film formation. For example, the fluoropolymerdispersions may comprise a mixture of first fluoropolymer particleshaving an average particle size (Z-average) of at least 180 nm incombination with second fluoropolymer particles that have an averageparticle size (Z-average particle diameter) of less than 180 nm,preferably an average particle size of not more than 0.9 or not morethan 0.7 times the average particle size (Z-average) of the firstfluoropolymer particles (as disclosed, for example, in U.S. Pat. No.5,576,381). Bimodal or multi-modal fluoropolymer dispersions can beconveniently obtained by blending the aqueous fluoropolymer dispersionof different fluoropolymer particle sizes together in the desiredamounts. The fluoropolymer population may not only be bimodal ormultimodal with respect to the particle sizes but may also be bimodal ormultimodal with respect to the fluoropolymers or the molecular weight ofthe fluoropolymers used. For example the first polymer having an averageparticle size of at least 180 nm may be a non-melt processablefluoropolymer and the second fluoropolymer having an average particlessize that is not more than 0.9 or not more than 0.7 times the averageparticle size of the first polymer may be a non-melt processable or amelt-processable fluoropolymer. Similarly the first and/or secondfluoropolymer may be a fluoroelastomer. In particular, dispersions ofnon-melt processable fluoropolymers may be mixed with aqueousdispersions of other fluoropolymers, in particular melt-processablefluoropolymers. Suitable dispersion of melt-processable fluoropolymersthat can be mixed with the non-melt processable fluoropolymerdispersions include dispersions of the following fluoropolymers:copolymers of TFE and a perfluorinated vinyl ether (PFA) and copolymersof TFE and HFP (FEP). Such dispersions may be monomodal, bi-modal ormultimodal as disclosed in e.g. EP 990 009 A1.

After the conclusion of the polymerization reaction, the dispersions maybe treated by anion exchange to remove the emulsifiers if desired.Methods of removing the emulsifiers from the dispersions byanion-exchange and addition of non-ionic emulsifiers are disclosed forexample in EP 1 155 055 B1, by addition of polyelectrolytes aredisclosed in WO2007/142888 or by addition of non-ionic stabilizers suchas polyvinylalcohols, polyvinylesters and the like.

The fluoropolymer content in the dispersions may be increased byupconcentration, for example using ultrafiltration as described, forexample in U.S. Pat. No. 4,369,266 or by thermal decantation (asdescribed for example in U.S. Pat. No. 3,037,953) or byelectrodecantation. The solid content of upconcentrated dispersions istypically about 50 to about 70% by weight.

Typically, dispersions subjected to a treatment of reducing the amountof fluorinated emulsifiers contain a reduced amount thereof, such as forexample amounts of from about 1 to about 500 ppm (or 2 to 200 ppm) basedon the total weight of the dispersion. Reducing the amount offluorinated emulsifiers can be carried out for individual dispersion orfor combined dispersion, e.g. bimodal or multimodal dispersions.Typically the dispersions are ion-exchanged dispersions, which meansthey have been subjected by an anion-exchange process to removefluorinated emulsifiers or other compounds from the dispersions. Suchdispersions typically contain trace amounts of trimethyl amine as a sideproduct from the anion-exchange process. Typically, such dispersionscontain from about 0.1 up to 50 ppm trimethylamine (based on the weightof the dispersion).

The dispersions may have a conductivity of at least 500 μS, typicallybetween 500 ILLS and 5,000 μS or between 500 and 1,500 μS. The desiredlevel of conductivity of the dispersion may be adjusted by adding a saltthereto such as for example a simple inorganic salt such as sodiumchloride or ammonium chloride, sulfates, sulfonates, phosphates and thelike. Also, the level of conductivity may be adjusted by adding ananionic non-fluorinated surfactant to the dispersion as disclosed in WO03/020836. Adding cationic emulsifiers to the dispersions is alsopossible, as described for example in WO 2006/069101.

Typical anionic non-fluorinated surfactants that may be used includesurfactants that have an acid group, in particular a sulfonic orcarboxylic acid group. Examples of non-fluorinated anionic surfactantsinclude surfactants that have one or more anionic groups. Anionicnon-fluorinated surfactants may include in addition to one or moreanionic groups, other hydrophilic groups such as polyoxyalkylene groupshaving 2 to 4 carbons in the oxyalkylene group (for example, polyoxyethylene groups). Typical non-fluorinated surfactants include anionichydrocarbon surfactants. The term “anionic hydrocarbon surfactants” asused herein comprises surfactants that include one or more hydrocarbonmoieties in the molecule and one or more anionic groups, in particularacid groups such as sulfonic, sulfuric, phosphoric and carboxylic acidgroups and salts thereof. Examples of hydrocarbon moieties of theanionic hydrocarbon surfactants include saturated and unsaturatedaliphatic groups having for example 6 to 40 carbon atoms, preferably 8to 20 carbon atoms. Such aliphatic groups may be linear or branched andmay contain cyclic structures. The hydrocarbon moiety may also bearomatic or contain aromatic groups. Additionally, the hydrocarbonmoiety may contain one or more hetero-atoms such as for example oxygen,nitrogen and sulfur.

Particular examples of non fluorinated, anionic hydrocarbon surfactantsinclude alkyl sulfonates such as lauryl sulfonate, alkyl sulfates suchas lauryl sulfate, alkylarylsulfonates and alkylarylsulfates, andalkylsulfosuccinates, fatty (carboxylic) acids and salts thereof such aslauric acids and salts thereof and phosphoric acid alkyl or alkylarylesters and salts thereof. Commercially available anionic hydrocarbonsurfactants that can be used include those available under the tradedesignation Polystep Al 6 (sodium dodecylbenzyl sulphonate) from StepanCompany, Germany; Hostapur SAS 30 (secondary alkyl sulphonate sodiumsalt), Emulsogen LS (sodium lauryl sulfate) and Emulsogen EPA 1954(mixture of C2 to C4 sodium alkyl sulfates) each available from ClariantGmbH, Germany; Edenor C-12 (Lauric acid) available from Cognis, Germany;and TRITON X-200 (sodium alkylsulfonate) available from Dow Chemical,Midland, Mich. Further suitable anionic surfactants include thesulfosuccinates disclosed in EP 1538177 and EP 1526142.

Non-fluorinated non-ionic surfactants may also be present in thedispersion, for example as the result of ion-exchange process to removethe fluorinated emulsifier or as the result of upcontentration processwhere non-ionic emulsifiers may have been added to increase thestability of the dispersions. Examples of non-ionic surfactants can beselected from the group of alkylarylpolyethoxy alcohols (although notbeing preferred), polyoxyalkylene alkyl ether surfactants, andalkoxylated acetylenic diols, preferably ethoxylated acetylenic diols,and mixtures of such surfactants.

Typically, the non-ionic surfactant or non-ionic surfactant mixture usedwill have an HLB (hydrophilic lypophilic balance) between 11 and 16.

In particular embodiments, the non-ionic surfactant of mixture ofnon-ionic surfactants corresponds to the general formula:

R₁O—[CH₂CH₂O]_(n)—[R₂O]_(m)—R₃  (V)

wherein R₁ represents a linear or branched aliphatic or aromatichydrocarbon group having at least 8 carbon atoms, preferably 8 to 18carbon atoms. In a preferred embodiment, the residue R1 corresponds to aresidue (R′)(R″)C— wherein R′ and R″ are the same or different, linear,branched or cyclic alkyl groups. In formula (V) above R2 represents analkylene having 3 carbon atoms, R2 represents hydrogen or a C1-C3 alkylgroup, n has a value of 0 to 40, m has a value of 0 to 40 and the sum ofn+m is at least 2. When the above general formula represents a mixture,n and m will represent the average amount of the respective groups.Also, when the above formula represents a mixture, the indicated amountof carbon atoms in the aliphatic group R₁ may be an average numberrepresenting the average length of the hydrocarbon group in thesurfactant mixture. Commercially available non-ionic surfactant ormixtures of non-ionic surfactants include those available from ClariantGmbH under the trade designation GENAPOL such as GENAPOL X-080 andGENAPOL PF 40. Further suitable non-ionic surfactants that arecommercially available include those of the trade designation TergitolTMN 6, Tergitol TMN 100X and Tergitol TMN 10 from Dow Chemical Company.Ethoxylated amines and amine oxides may also be used as emulsifiers.

Typical amounts are 1 to 12% by weight based on the weight of thedispersion. Further non fluorinated, non-ionic surfactants that can beused include alkoxylated acetylenic diols, for example ethoxylatedacetylenic diols. The ethoxylated acetylenic diols for use in thisembodiment preferably have a HLB between 11 and 16. Commerciallyavailable ethoxylated acetylenic diols that may be used include thoseavailable under the trade designation SURFYNOL from Air Products,Allentown, Pa. (for example, SURFYNOL 465). Still further usefulnon-ionic surfactants include polysiloxane based surfactants such asthose available under the trade designation Silwet L77 (Crompton Corp.,Middlebury, Conn.) Amine oxides are also considered useful asstabilizing additives to the fluoropolymer dispersions described herein.

Other examples of non-ionic surfactants include sugar surfactants, suchas glycoside surfactans and the like.

Another class of non-ionic surfactants includes polysorbates.Polysorbates include ethoxylated, propoxylated or alkoxylated sorbitansand may further contain linear cyclic or branched alkyl residues, suchas but not limited to fatty alcohol or fatty acid residues. Examples ofpolysorbates include those according to general structure:

wherein R represents a residue OC—R1 and wherein R1 is a linear,branched, cyclic, saturated or unsaturated, preferably saturated, alkyl,alkoxy or polyoxy alkyl residue comprising 6 to 26, or 8 to 16 carbonatoms. In the above represented formula, n, x, y, and z are integersincluding 0 and n+x+y+z is from 3 to 12. The above general formularepresents monoesters but di-, tri- or tetraester are also encompassed.In such case one or more of the hydroxyl hydrogens is replaced by aresidue R, wherein the residue R has the same meaning as described abovefor the monoester.

Useful polysorbates include those available under the trade designationPolysorbate 20, Polysorbate 40, Polysorbate 60 and Polysorbate 80.Polysorbate 20, is a laurate ester of sorbitol and its anhydrides havingapproximately twenty moles of ethylene oxide for each mole of sorbitoland sorbitol anhydrides. Polysorbate 40 is a palmitate ester of sorbitoland its anhydrides having approximately twenty moles of ethylene oxidefor each mole of sorbitol and sorbitol anhydrides. Polysorbate 60 is amixture of stearate and palmitate esters of sorbitol and its anhydrideshaving approximately twenty moles of ethylene oxide for each mole ofsorbitol and sorbitol anhydrides.

Polyelectrolytes, such as polyanionic compounds (for example polyanionicpoly acrylates) may also be added to the dispersion in addition orinstead of the surfactants described above.

The dispersions may further contain ingredients that may be beneficialwhen coating or impregnating the dispersion on a substrate, such asadhesion promoters, friction reducing agents, pigments and the like.Optional components include, for example, buffering agents and oxidizingagents as may be required or desired for the various applications. Thedispersions of the present invention can be used to produce finalcoating compositions for coating various substrates such as metals,fluoropolymer layers and fabrics, such as, for example, glassfiber-based fabrics. Such fabrics may be used as architectural fabrics.Generally, the fluoropolymer dispersions will be blended with furthercomponents typically used to produce a final coating composition. Suchfurther components may be dissolved or dispersed in an organic solventsuch as toluene, xylene and the like. Typical components that are usedin a final coating composition include polymers such as polyamideimides, polyimides or polyarylene sulphides or inorganic carbides, suchas silicium carbide, and metal oxides. They are typically employed asheat resistant adhesion promoters or primers. Still further ingredientssuch as pigments and mica particles may be added as well to obtain thefinal coating composition. The fluoropolymer dispersions typicallyrepresent about 10 to 80% by weight of the final composition. Details oncoating compositions for metal coatings and components used therein havebeen described in e.g. WO 02/78862, WO 94/14904, EP 1 016 466 A1, DE 2714 593 A1, EP 0 329 154 A1, WO 0044576, and U.S. Pat. No. 3,489,595.

The fluoropolymer dispersions may be used, for example, to laminate,coat and/or impregnate a substrate. The substrate or the treated surfacethereof may be an inorganic or organic material. The substrate may be,for example a fiber, a fabric, a granule or a layer. Typical substratesinclude organic or inorganic fibers, preferably glass fibers, organic orinorganic fabrics, granules (such as polymer beads) and layerscontaining one or more organic polymers, including, for example,fluoropolymers. The fabrics may be woven or non-woven fabrics. Thesubstrate may also be a metal or an article containing a metal surfaceor a fluoropolymer surface or layer, such as but not limited to PTFEsurface or layers.

The fluoropolymer dispersions may also be used to make “compounds”.“Compounds” as use here are solid compositions comprising one or morefluoropolymers as described herein and one or more fillers andoptionally further additives. Typically, “compounds” may be in the formof particles (like granules or pellets) or in the form of sheets. The“compounds” may have a diameter or longest axis of from at least 1 μm orat least 5 or at least 50 μm or at least 500 μm or at least 5,000 μm.For making “compounds” a homogeneous distribution of fluoropolymer andfiller are desired. This however is often difficult to achieve by dryblending and extruding or blending during extrusion. In one embodiment afluoropolymer dispersion as described above is used to make “compounds”.In this embodiment a pH-dependent surfactant is added to the dispersion,at a pH at which the surfactant is in a form in which it stabilises thedispersion. The filler are then added to the dispersion and the mixtureis shaken or stirred to provide a homogeneous distribution of the fillermaterial in the dispersion. The fluoropolymer is then brought tocoagulation, for example, by changing the pH to a level at which thepH-dependent surfactant no longer stabilises the dispersion. Thecoagulated fluoropolymer particles contain the filler material andhomogeneous fluoropolymer compounds may be obtained. Suitable fillerinclude carbon-based materials like for example soot, graphite, carbonblacks, carbon fibers, glass fibers, metals and metal alloys and thelike. Instead of fillers additives may be incorporated into thecompounds in the same way. Typically, fillers and or additives may bepresent in amounts of from 0.1 to up to 30% by weight based on theweight of the “compound”.

pH-dependent surfactant are surfactants that exist in a ionic form at acertain pH level and in a non-ionic form at a different pH level. Forexample, a pH-dependent surfactant may be cationic at a pH below a pH of6 or at 5 or at 4 and it may be non-ionic at a pH greater than 7 or 8 or10 or 11. pH-dependent surfactants that may be used herein are describedin detail for example in WO 2008/134138 to Dadalas et al which isincorporated herein by reference. pH-dependent surfactants include, forexample, amine ethoxylates, for instance those provided under the tradedesignation GENAMIN from Clariant, Basel, Switzerland or TRITON RW fromDow Chemicals. Amine ethoxylates typically have a structure according tothe general formula R1(R2)-N—R3.

In the above formula R1 and R2 represent independently from each othernon-polar residues, like, for example, branched, linear or cyclic alkylor oxoalkyl or polyoxyalkyl residues. R3 represents a polyoxylkyleneresidue such as a polyethoxylate or a polypropoxylate or a combinationthereof.

For melt processing and making shaped articles the tetrafluoroethylenecopolymers are used in dry form and therefore have to be separated fromthe dispersion. The tetrafluoroethylene copolymers described herein maybe collected by deliberately coagulating them from the aqueousdispersions. In one embodiment, the aqueous emulsion is stirred at highshear rates to deliberately coagulate the polymers. In anotherembodiment, a coagulating agent, such as for example, an ammoniumcarbonate, a polyvalent organic salt, a mineral acid, a cationicemulsifier or an alcohol or a combination or a sequence thereof may beadded to the aqueous emulsion to deliberately coagulate the polymers.Agglomerating agents such as hydrocarbons like toluenes, xylenes and thelike may be added to increase the particle sizes and to formagglomerates. The use of agglomerating agents, in particular in thepresence of mineral acids and while stirring lead to the formation ofspherical particles.

Drying of the polymer particles obtained by the deliberate coagulationor by agglomeration can be carried out at an optional temperature, suchas for example, drying within a range of from 100° C. to 300° C. Thecoagulated and dried polymers (i.e., secondary particles) according tothe present disclosure have an average particle size (number average) ofgreater than 150, 250, 300, 400, 500, 1000, or even 1500 μm(micrometers). Particle sizes of coagulated particles can be determinedby electron microscopy. The average particle sizes can be expressed asnumber average by standard particle size determination software. Theparticle sizes may be increased by melt-pelletizing.

The coagulated fluoropolymers or melt pellets may be subjected to afluorination treatment as described, to remove thermally unstable endgroups. Unstable end groups include —CONH2, —COF and —COOH groups.Fluorination is conducted so as to reduce the total number of those endgroups to less than 100 per 10⁶ carbon atoms in the polymer backbone.Suitable fluorination methods are described for example in U.S. Pat. No.4,743,658 or DE 195 47 909 A1. The amount of end groups can bedetermined by IR spectroscopy as described for example in EP 226 668 A1.

For making shaped articles the tetrafluoroethylene copolymers arebrought to the melt (optionally after having been pelletized) and thenprocessed from the melt to shaped articles, for example, by injectionmolding, blow molding, melt extruding, melt spinning and the like.Additives may be added before or during the melt processing. Sucharticles include, for example, fibers, films, O-rings, containers, tubesand the like. Typically, the additives may be present in amounts of 0%,greater than 0% and less than 50% by weight, or less than 20% by weightor less than 10% by weight so that the shaped article may bepredominantly made from the tetrafluoroethylene copolymers.

Advantages and embodiments of this invention are further illustrated bythe following list of embodiments and examples, but the particularmaterials and amounts thereof recited in these examples, as well asother conditions and details, should not be construed to unduly limitthis invention. All parts and percentages are by weight unless otherwiseindicated.

List of Specific Embodiments

1. A tetrafluoroethylene copolymer comprising repeating units derivedfrom tetrafluoroethylene (TFE) and having a melting point of at least317° C., a melt flow index (MFI) at 372° C. and a 5 kg load (MFI 372/5)of from about 0.60 g/10 min up to about 15 g/10 min, and comprising from0.12 to 1.40% by weight based on the weight of the copolymer of unitsderived from one or more perfluorinated comonomers and wherein theperfluorinated comonomers comprise one or more perfluorinated alkylvinyl ether or perfluorinated alkyl allyl ether wherein the alkyl groupof the perfluorinated vinyl or allyl ether is interrupted by at leastone oxygen atom.2. The copolymer of 1 wherein the perfluorinated alkyl vinyl or alkylallyl ether corresponds to the general formula

CF₂═CF—(CF₂)_(n)—O—Rf  (I),

or

CF₂═CF—(CF₂)_(n′)—O—Rf′—O—(CF₂)_(m)—CF═CF₂  (II),

wherein n represents either 1 or 0,n′ and m represent, independently from each other either 1 or 0,Rf represents a linear or branched, cyclic or acyclic perfluorinatedalkyl residue containing at least one catenary oxygen atom andcontaining up to 8 carbon atoms, andRf′ represents a linear, branched, cyclic or acyclic perfluorinatedalkylene unit that may or may not contain one or more catenary oxygenatoms and that has up to 8 carbon atoms.3. The copolymer of either one of 1 or 2 having an elongation at breakof at least 10% or at least 20%.4. The copolymer of any one of 1 to 3 having a tensile strength at breakof at least 10 MPa.5. The copolymer of any one of 1 to 4 having a melting point of at least319° C. or at least 321° C.6. The polymer of any one of 1 to 5 having a melting point between 321°C. and 329° C.7. The copolymer of any one of 1 to 6 wherein the perfluorinatedcomonomer is selected fromCF₂═CF—(CF₂)_(n)—O—Rf and wherein Rf represents a linear or branchedperfluorinated alkyl residue containing one catenary oxygen and up to 6carbon atoms.8. The copolymer of any one of 1 to 6 wherein the perfluorinatedcomonomer is selected fromCF₂═CF—(CF₂)_(n)—O—Rf and wherein Rf represents a linear or branchedperfluorinated alkyl residue containing one catenary oxygen and up to 6carbon atoms and wherein the copolymer has an MFI (372/5) between 0.60and 5 g/10 min.9. The copolymer of any one of 1 to 6 wherein the perfluorinatedcomonomer is selected from

CF₂═CF—(CF₂)_(n)—O—Rf and wherein Rf represents a linear or branchedperfluorinated alkyl residue containing one catenary oxygen and up to 6carbon atoms, wherein the copolymer has an MFI (372/5) between 0.60 and5 g/10 min and wherein the copolymer comprises from about 0.2 to about1.4% by weight based on the weight of the copolymer, preferably fromabout 0.4 up to about 1.0% by weight based on the weight of thecopolymer.

10. The copolymer according to any one of 1 to 6 wherein theperfluorinated comonomer is selected from CF₂═CF—(CF₂)_(n)—O—Rf andwherein Rf represents a linear or branched perfluorinated alkyl residuecontaining at least two catenary oxygen atoms and up to 6 carbon atoms.11. The copolymer according to any one of 1 to 6 wherein theperfluorinated comonomer is selected from CF₂═CF—(CF₂)_(n)—O—Rf andwherein Rf represents a linear or branched perfluorinated alkyl residuecontaining at least two catenary oxygen atoms and up to 6 carbon atoms,wherein the copolymer has an MFI (372/5) between 0.8 and 12.0 g/10 min.12. The copolymer according to any one of 1 to 6 wherein theperfluorinated comonomer is selected from CF₂═CF—(CF₂)_(n)—O—Rf andwherein Rf represents a linear or branched perfluorinated alkyl residuecontaining at least two catenary oxygen atoms and up to 6 carbon atoms,wherein the amount of perfluorinated comonomer is from about 0.12% byweight to about 1.40 by weight, preferably from about 0.20 up to about1.0% by weight, more preferably up to about 0.9% by weight based on theweight of the copolymer.13. The copolymer according to 12 wherein the copolymer has an MFI(372/5) between 0.8 and 12.0 g/10 min.14. The copolymer according to any one of 2 to 6 wherein theperfluorinated comonomer has the formulaCF₂═CF—(CF₂)_(n′)—O—Rf′—O—(CF₂)_(m)—CF═CF₂.15. The copolymer according to any one of 1 to 14 wherein the remainderof the copolymer is comprised of units derived from TFE.16. The copolymer according to 15 wherein up to 30% by weight of theunits derived from TFE are replaced by CTFE.17. Method of making a shaped article comprising:providing a composition comprising the copolymer according to any one of1 to 16, subjecting the composition to melt-processing selected frommelt extrusion, melt spinning, injection molding and melt blowing.18. A shaped article comprising the polymer according to anyone of 1 to16.19. The shaped article of 18 being selected from fibers, films, O-rings,containers.20. A composition comprising a copolymer according to any one of 1 to 16wherein the composition is an aqueous dispersion.21. Method of making tetrafluoroethylene copolymers that aremelt-processable and have an elongation at break of at least 20% and atensile strength at break of at least 10 MPa and a melting point of atleast 317° C., or at least 319° C., or at least 321° C., and an MFI(375/5) of from 0.60 g/10 min up to about 15 g/10 min comprising:polymerizing TFE in an aqueous medium in the presence of an effectiveamount of a perfluorinated comonomer as defined in claim 1.22. The method of 21 comprising polymerising TFE in an aqueous emulsionpolymerisation or suspension polymerisation in the presence of aninitiator.23. The method of 21 comprising polymerising TFE in an aqueous emulsionpolymerisation in the presence of at least one initiator and at leastone emulsifier.24. The method of 21 to 23 wherein the effective amount comprises from0.12 to 1.40% by weight based on the weight of TFE.25. The method of any one of 21 to 24 wherein the perfluorinated alkylvinyl or alkyl allyl ether corresponds to the general formula

CF₂═CF—(CF₂)_(n)—O—Rf  (I),

or

CF₂═CF—(CF₂)_(n′)—O—Rf′—O—(CF₂)_(m)—CF═CF₂  (II),

wherein n represents either 1 or 0,n′ and m represent, independently from each other either 1 or 0,Rf represents a linear or branched, cyclic or acyclic perfluorinatedalkyl residue containing at least one catenary oxygen atom andcontaining up to 8 carbon atoms, andRf′ represents a linear, branched, cyclic or acyclic perfluorinatedalkylene unit that may or may not contain one or more catenary oxygenatoms and that has up to 8 carbon atoms.26. The method of any one of 21 to 25 having a melting point of at least319° C. or at least 321° C.27. The method of any one of 21 to 26 having a melting point between321° C. and 329° C.28. The method of any one of 21 to 27 wherein the perfluorinatedcomonomer is selected fromCF₂═CF—(CF₂)_(n)—O—Rf and wherein Rf represents a linear or branchedperfluorinated alkyl residue containing one catenary oxygen and up to 6carbon atoms.29. The method of any one of 21 to 28 wherein the perfluorinatedcomonomer is selected fromCF₂═CF—(CF₂)_(n)—O—Rf and wherein Rf represents a linear or branchedperfluorinated alkyl residue containing one catenary oxygen and up to 6carbon atoms and wherein the copolymer has an MFI (372/5) between 0.60and 5 g/10 min.30. The method of any one of 21 to 29 wherein the perfluorinatedcomonomer is selected fromCF₂═CF—(CF₂)_(n)—O—Rf and wherein Rf represents a linear or branchedperfluorinated alkyl residue containing one catenary oxygen and up to 6carbon atoms, wherein the copolymer has an MFI (372/5) between 0.60 and5 g/10 min and wherein the effective amount comprises from at leastabout 0.2 to about 1.4% by weight based on the weight of TFE, preferablyfrom at least about 0.4 up to about 1.0% by weight based on the weightof TFE.31. The method according to any one of 21 to 27 wherein theperfluorinated comonomer is selected from CF₂═CF—(CF₂)_(n)—O—Rf andwherein Rf represents a linear or branched perfluorinated alkyl residuecontaining at least two catenary oxygen atoms and up to 6 carbon atoms.32. The method according to any one of 21 to 27 wherein theperfluorinated comonomer is selected from CF₂═CF—(CF₂)_(n)—O—Rf andwherein Rf represents a linear or branched perfluorinated alkyl residuecontaining at least two catenary oxygen atoms and up to 6 carbon atoms,wherein the copolymer has an MFI (372/5) between 0.8 and 12.0 g/10 min.33. The method according to any one of 21 to 27 wherein theperfluorinated comonomer is selected from CF₂═CF—(CF₂)_(n)—O—Rf andwherein Rf represents a linear or branched perfluorinated alkyl residuecontaining at least two catenary oxygen atoms and up to 6 carbon atoms,wherein the effective amount of perfluorinated comonomer is from atleast about 0.12% by weight to at least about 1.40 by weight, preferablyfrom at least about 0.20 up to at least about 1.0% by weight based onthe weight of TFE.34. The method according to 33 wherein the copolymer has an MFI (372/5)between 0.8 and 12.0 g/10 min.35. The method according to any one of 21 to 27 wherein theperfluorinated comonomer has the formulaCF₂═CF—(CF₂)_(n′)—O—Rf′—O—(CF₂)_(m)—CF═CF₂.36. The method according to any one of 21 to 35 wherein the remainder ofthe monomers TFE.37. The method according to 35 wherein up to 30% by weight of the TFE isreplaced by CTFE.

Test Procedures: Melt Flow Index (MFI):

Melt flow index was measured with a Gottfert melt indexer according toDIN EN ISO 1133 using a 5 kg load and a temperature of 372° C. (MFI372/5). The extrusion time was one hour.

Average Particle Size:

Average particle size of polymer particles as polymerized was measuredby electronic light scattering using a Malvern Autosizer 2c inaccordance with ISO 13321. This method assumes a spherical particalsize. The average particle sizes are expressed as the Z-average.

Solid Content:

The solid content (fluoropolymer content) of the dispersions wasdetermined gravimetrically according to ISO 12086. A correction for nonvolatile inorganic salts was not carried out.

Comonomer Content:

The comonomer content in the polymers described herein was determined byinfrared spectroscopy using a Thermo Nicolet Nexus FT-IR spectrometer.In the case of the MV-31 containing polymers the comonomer content in %wt was calculated as 1.48× the ratio of the sum of the 891 and the 997cm⁻¹ absorbance to the 2365 cm⁻¹ absorbance. All other comonomercontents were calculated as 0.95× the ratio of the 993 cm⁻¹ absorbanceto the 2365 cm⁻¹ absorbance (compare U.S. Pat. No. 6,395,848).

Melting Point:

Melting points were determined by DSC (a Perkin Elmer differentialscanning calorimeter Pyris 1) according to ASTM D 4591. 5 mg sampleswere heated at a controlled rate of 10° C./min to a temperature of 380°C. by which the first melting temperature was recorded. The samples werethen cooled at a rate of 10° C./min to a temperature of 300° C. and thenreheated at 10° C./min to a temperature at 380° C. The melting pointobserved at the second heating period was recorded and is referred toherein as the melting point of the polymer (melting point of the oncemolten material).

Elongation at Break and Tensile Strength at Break:

Elongation at break and tensile strength at break were determinedaccording to DIN EN ISO 527-1 using a Zwick Tensile Tester. Testspecimen were elongated at a speed of 50 mm/min at room temperature (22°C.+/−3° C.).

Test samples were prepared as follows: dried polymer samples were givenin a circular mold having a diameter of 130 mm and then press-molded at360° C. and 53 bar for 2 minutes. The disks were removed from the moldand kept at 23° C. and 50% relative humidity for 16 hours. Test specimen(according to DIN ISO 12086) were cut from the disks and subjected totensile tester.

Samples which broke when removing the disks from the molds or whencutting the test specimen from the disks could not be subjected tomechanical testing. Those samples were regarded to have a tensilestrength and elongation at break of 0.

Comparative Example 1 Copolymer of TFE and PPVE

The reactor described in example 1 was filled with 30 liters deionizedwater and 190 g of a anqueous solution containing 30% by weight of theemulsifier CF3-O—(CF2)3-O—CHF—CF2-COONH4. After degassing the system thereactor was heated to 60° C. and ethane was introduced to reach 0.345bar, followed by charging the reactor with 54 g PPVE-1. TFE wasintroduced until a pressure of 12 bar abs was reached. 6.0 g of ammoniumperoxodisulfate (APS) dissolved in 50 ml water were introduced toinitiate the polymerization. The pressure was kept constant by feedingTFE and additional PPVE-1 in a weight ratio of 1:0.010. When a totalamount of 12 kg TFE was consumed the polymerization was stopped byclosing the TFE feed. The reactor was vented and discharged. 41.8 kg ofdispersion with a solids content of 29.7% were obtained.

The polymer had the following characteristics:

Particle size (in dispersion): 102 nm.Melting point: 319° C.MFI (372° C./5 kg): 6.4 g/10 min.Comonomer content: 0.83 wt %.Mechanical properties: elongation and tensile: 0* * as used herein aboveand below means: testing was not possible because samples were toobrittle. No specimen for measurement could be prepared.

Comparative Example 2 Copolymer of TFE and PPVE

Comparative Example 1 was repeated with the following changes: 6.0 g ofinitiator and 50 g of comonomer were charged. Ethane was added to give apressure of 0.345 bar. A dispersion with a solid content of 29.4% wasobtained.

The polymer had the following characteristics:

Particle size (dispersion): 99 nm.Melting point: 323° C.MFI (372° C./5 kg): 5.3 g/10 min.Comonomer content: 0.53 wt %.Elongation at break and Tensile strength at break: 0*

Comparative examples 1 and 2 show that a polymer having a melting pointof greater than 317° C. can be prepared that can be melt-processed intoa shaped article cannot be made by copolymerizing TFE with PPVE.

Example 1 Copolymer of TFE and MV-31

A 40 liter volume vertical stainless steel reactor equipped with animpeller stirrer working at 240 rpm was filled with 29 liters deionizedwater and 147 g of a 30 wt % solution of ammonium perfluoro2,6-dioxa-nonanoic acid as emulsifier. After degassing the system thereactor was heated to 63° C. and ethane was introduced to reach apressure of 0.26 bar, followed by charging the reaction with 72 g MV-31.TFE was introduced to the reactor until a pressure of 13 bar abs wasreached. 1.3 g of the polymerization initiator ammonium peroxodisulfate(APS), dissolved in 50 ml water, were introduced to initiate thepolymerization. The pressure was kept constant by feeding TFE andadditional MV-31 in a weight ratio of 1:0.011. When a total amount of 12kg TFE had been consumed the polymerization was stopped by closing theTFE feed. The reactor was vented and discharged. 42 kg of dispersionwith a solids content of 29.2% were obtained. The polymer was isolatedby coagulation with hydrochloric acid, agglomeration with gasoline,washing and drying in an oven.

The polymer had the following characteristics:

Particle size (of the dispersion): 115 nm.Melting point: 322° C.MFI (372° C./5 kg): 0.88 g/10 min.Comonomer content: 0.62 wt %.Elongation at break: 372%Tensile strength at break: 23.6 MPa.

Example 2 Copolymer of TFE and MV-31

Example 1 was repeated with the following changes: 2.5 g of initiatorand 258 g of comonomer were used. Ethane was added to give a pressure of0.45 bar. A dispersion with a solid content of 29.1% was obtained.

The polymer had the following characteristics:

Particle size (of the dispersion): 121 nm.Melting point: 325° C.MFI (372° C./5 kg): 3.7 g/10 min.Comonomer content: 0.66 wt %.Elongation at break: 38%Tensile strength at break: 13.9 MPa.

Comparative Example 3

The reaction described in example 1 was repeated with the followingchanges: The amount of comonomer was 311 g. Ethane was introduced intothe reactor to reach a pressure of 0.6 bar. 4.0 g of initiator was used.A dispersion with a solid content of 29.2% was obtained.

The polymer had the following properties:

particle size: 120 nm,

MFI: 16.5,

comonomer content: 0.65% wt,

mp.: 321° C.

mechanical properties: elongation and tensile strength at break: 0*

A comparison of examples 1 and 2 with comparative examples 3 shows thatan MFI (372/5) above 15 leads to brittle materials with no suitablemechanical properties.

Example 3 Copolymer of TFE and MA-21.111

The reactor described in example 1 was filled with 30 liters deionizedwater and 147 g of a 30 wt % solution of emulsifier. After degassing thesystem the reactor was heated to 85° C. and ethane was introduced toreach 0.100 bar, followed by charging the reactor with 168 g MA 21.111as a 50% emulsion in water. TFE was introduced until a pressure of 13bar abs was reached. 6.25 g of ammonium peroxodisulfate (APS) dissolvedin 125 ml water were introduced to initiate the polymerization. Duringthe polymerization additional 1.5 g/h APS were added as a 5% solution indeionised water. The pressure was kept constant by feeding TFE andadditional 336 g MA 21.111 (as a 50% emulsion) in a weight ratio of1:0.056. When a total amount of 12 kg TFE was consumed thepolymerization was stopped by closing the TFE feed. The reactor wasvented and discharged.

The polymer had the following characteristics:

particle size (dispersion): 148 nm,melting point: 319° C.,MFI: 3.6 g/10 min;comonomer content: 0.14 wt %,elongation at break: 295%,tensile strength: 13.4 MPa.

Example 4 Copolymer of TFE and MA-211.111

The reactor described in example 1 was filled with 30 liters deionizedwater and 147 g of a 30 wt % solution of the emulsifier. After degassingthe system the reactor was heated to 85° C. and ethane was introduced toreach 0.090 bar, followed by charging the reactor with 180 g MA 211.111as a 50% emulsion in water. TFE was introduced until a pressure of 13bar abs was reached. 6.20 g of ammonium peroxodisulfate (APS) dissolvedin 125 ml water were introduced to initiate the polymerization. Duringthe polymerization additional 1.6 g/h APS were added as a 4% solution indeionised water. The pressure was kept constant by feeding TFE andadditional 368 g MA 211.111 (as an 50% wt. emulsion) in a weight ratioof 1:0.0613. When a total amount of 12 kg TFE was consumed thepolymerization was stopped by closing the TFE feed. The reactor wasvented and discharged.

The polymer had the following characteristics:

Particle size (dispersion): 154 nm.Melting point: 319° C.MFI 5.0 g/10 min;

Comonomer: 0.14 wt %,

Elongation at break: 130%,Tensile strength: 13.5 MPa.

1. A tetrafluoroethylene copolymer comprising repeating units derivedfrom tetrafluoroethylene and from 0.12 to 1.40% by weight, based on thetotal weight of the copolymer, of units derived from a comonomer of thegeneral formula:CF₂═CF—(CF₂)_(n′)—O—Rf′—O—(CF₂)_(m)—CF═CF₂ wherein n′ and m represent,independently from each other, either 1 or 0; and Rf′ represents alinear, branched, cyclic or acyclic perfluorinated alkylene unit thatmay contain one or more ether oxygen atoms and that has up to 8 carbonatoms; further wherein the copolymer has a melting point of at least317° C., a melt flow index at 372° C. and a 5 kg load of from about 0.60g/10 min up to about 15 g/10 min.
 2. The copolymer of claim 1 having anelongation at break of at least 10%.
 3. The copolymer of claim 1 havinga tensile strength at break of at least 10 MPa.
 4. The copolymer ofclaim 1 having a melting point of at least 319° C. or at least 321° C.5. The copolymer according to claim 1, further comprising up to 30% byweight, based on the total weight of the copolymer, of units derivedfrom chlorotrifluoroethylene.
 6. A method of making a shaped articlecomprising: providing a composition, the composition comprising acopolymer according to claim 1, and subjecting the composition tomelt-processing selected from melt extrusion, melt spinning, injectionmolding and melt blowing.
 7. A shaped article comprising a copolymeraccording to claim
 1. 8. A composition comprising an aqueous dispersionof a copolymer according to claim
 1. 9. A method of makingtetrafluoroethylene copolymers that are melt-processable and have anelongation at break of at least 20% and a tensile strength at break ofat least 10 MPa and a melting point of at least 317° C., or at least319° C., or at least 321° C., and an MFI (375/5) of from about 1 toabout 15 g/10 min comprising: polymerising tetrafluoroethylene in anaqueous medium in the presence of a comonomer according to claim 1, toprovide a copolymer according to claim 1.